Ground penetrating radar is a non-destructive geophysical
method that produces a continuous cross-sectional profile or record of
subsurface features, without drilling, probing, or digging.
Ground penetrating radar (GPR) profiles are used for
evaluating the location and depth of objects and to investigate the presence
and continuity of subsurface conditions and features.
Ground penetrating radar operates by transmitting pulses of
ultra high frequency radio waves down into the ground through an antenna.
Several antennae are available ranging in centre frequency from 25 to 1500 MHz.
The selection of antennae is dependent on the soil conditions and depth of
When the transmitted signal enters the ground, it contacts
objects or subsurface strata with different electrical conductivities and
dielectric constants. Part of the ground penetrating radar waves reflects off
the object or interface; while the rest of the waves pass through to the next
The reflected signals return to the antenna, pass through
the antenna, and are received by the digital control unit. Two-way travel time
is used to calculate the reflector depth assuming that the velocity of the
material being tested is reasonably estimated or known.
The control unit registers the reflections against two-way
travel time in nanoseconds and then amplifies the signals. The output signal
voltage peaks are plotted on the ground penetrating radar profile as different
colour bands by the digital control unit.
For each reflected wave, the radar signal changes polarity
twice. These polarity changes produce three bands on the radar profile for each
interface contacted by the radar wave. This forms the basis of collating